Unit 2 - Forces + Motion Flashcards
What is the unit for weight
Newtons (N)
Weight is a force
Unit for distance
Metre (m)
Unit for velocity
Metre/second (m/s)
Unit for acceleration
Metres per second per second (m/s²)
Unit of measure for any force
Newton (N)
Is speed scalar or vector ?
Speed is a scalar quality (does not have a direction)
Is velocity scalar or vector?
Velocity is a vector quantity as it has a direction.
ie. Travelling at 4m/s north = 4m/s velocity
Travelling at 4m/s south = -4m/s velocity
Is force vector or scalar ?
All force has a direction and therefore force is a vector quantity
Average speed (m/s) =
Distance moved (m) / time taken (s)
Acceleration (m/s²) =
Change in velocity (m/s) / time taken (s)
*deceleration is negative (slowing down)
In a distance/time graph, the gradient =
The speed.
Speed = distance/time
In a distance/time graph, a horizontal line means …
The object is still
In a velocity/time graph, the gradient =
Acceleration
Acceleration = v-u / time v = start velocity u = new velocity
In a velocity/time graph, a horizontal line means ..
That the object is travelling at constant velocity
The area underneath a velocity/time graph =
The distance travelled
What is relationship between force, mass, and acceleration
Force (N) = mass (kg) X acceleration (m/s²)
Relationship between weight, mass, and gravity (g)
Weight (N) = mass (kg) X gravity (g)
When does an object reach terminal velocity ?
When the forces acting against an object (drag or resistance) equal the gravitational pull of the object
What factors affect a vehicles stopping distance ?
Speed, mass of car, road conditions, reaction time
What is the thinking distance ?
The distance travelled between the driver reacting and when they actually hit the brakes
What factors affect thinking distance
SPEED, mental state of driver (drunk, tired, distracted), visibility
Momentum =
Momentum (kg m/s) = mass (kg) X velocity (m/s)
Unit of measure for momentum
Kilogram metre/second (kg m/s)
Newtons 1st law
Objects will stay stationary, or continue to move with constant speed, unless an unbalanced force acts upon then.
Newtons 2nd law
The acceleration produced by a force when it acts on a body is proportional to the force and takes place in the same direction as the force
Newtons 3rd law **
To every force, there is an equal and opposite reaction force
Law of conservation of momentum
So long as no external forces are acting on the objects involved, the total momentum before a collision is the same as the total momentum after the collision
Relationship between force, change in momentum, and time
Force (N) = change in momentum (kg m/s) / time taken (s)
What is the unit for mass
Kilogram (kg)
What is friction
A force that opposes motion
What is instantaneous speed
Speed in the exact moment
What effects can a force have on a body?
Changes in speed, shape, or direction
What are the forces acting on a falling object
Downward: weight (gravitational)
Upward : air resistance (drag)
How to use the conservation of momentum to calculate the mass, velocity or momentum of objects
Momentum (kg m/s) = mass (kg) x velocity(m/s)
Velocity= momentum / mass
Mass= momentum / velocity
If a bullet with a mass of 0.2g is shot from a gun at 100 m/s to work out its momentum we do 0.2g x 100 m/s = 20 g m/s.
How do seat belts reduce risk (momentum)
force = change in momentum / time
The stretchy material that seat belts are made of make the time taken to come to a complete stop take longer. By increasing the time taken to stop, it decrease the amount of force exerted on the passenger (*)
Unit for moment
Newtons per metre (N/M)
Moment =
Moment = force (N) X perpendicular distance from pivot (M)
Where in an object does weight act?
The weight of a body acts through its centre of gravity
What is Hookes law
Hooke’s law states that the extension is proportional to the applied force (load), provided that the elastic limit is not exceeded
What is elastic behaviour
Elastic behaviour is the ability of a material to recover its original shape after the forces causing deformation (load) has been removed
What is the different between the orbits of comets, moons, and planets
The orbit of moons and planets are described as circular (even though they are slightly elliptical).
Planets orbit starts
Moons orbit planets
Comets orbit stars, however their orbit is EXTREMELY elliptical
Orbital speed (Km per day) =
(2π X orbital radius (km)) / time period (days)
What is the universe
The universe is a large collection of billions of galaxies
What is a galaxy
A galaxy is a large collection of billions of stars
Where is our solar system
In the Milky Way Galaxy
What is g on earth
10N/Kg
What is g on the moon
1.6 N/Kg
What is gravitational field strength
Gravitational field strength is what causes objects to have weight. It is different on all planets/moons/comets. The more mass an object has, the more gravitational field strength it has
What is the principle of moments
When an object is in equilibrium (balanced), the sum of the clockwise moment about a point must be equal to the sum of the anti-clockwise moment about the same point
Experiment to investigate how extension varies with applied forces for helical Spring, metal wires, and rubber bands
Attach a spring to a newton meter and measure its length
Add a 50g weight and measure again
continue to add another weight and take another measurement
Do this up to 400g
by plotting a graph from the results from this you can see the extension increases with force; as each time a weight is added the spring gets longer.
How to the upward forces on a light beam, supported at its ends, vary depending on the position of heavy object placed on a beam
This means you need to understand that if you have say a plank of wood being held in balance by springs pushing up at the ends and you put a weight on the beam, the springs would have to exert more force as they need to equal the downward force.
